"You can only do so many projects for other people before you start thinking, wouldn't it be lovely to do something for yourself?" says designer Jonathan Tuckey, of the north London family home he created on the site of a former steelworks.

"The steel company that used to be here was a family business and they'd made a few worktops for residential projects we've done. I'd been through the door a few times and said, 'If there ever comes a stage when you move on, let us know...' " Three years later, Tuckey got a call, which set in motion a further three years of design work, planning applications and building, with the help of a team of Gujarati craftsmen from Harrow, for whom nothing was impossible.

The result is an unexpected creation, off Kilburn High Road, behind an industrial facade complete with old signage for the steelworks. It has the proportions of a warehouse and the raw, unpolished aesthetic of a former factory, coupled with lots of playful touches - there's an indoor stream by the dining table where the children can float boats, a garden plunge pool and an open-plan family bathroom without electricity. "How appropriate it will be in 10 years' time I don't know," Tuckey admits. "It will be interesting to see..."

The home Tuckey shares with his wife, Annabel, a teacher, and their two young daughters, Tasmina and Thea, is built around a courtyard garden. "We looked at a lot of traditional domestic Islamic and Japanese architecture, where the garden is brought right into the centre of the house," says Tuckey. "Originally, the property had no garden but it was important to us."

Tuckey's plot was a standard five-metre wide, two-up, two-down house at the front (now housing his architectural practice), which had been extended to the back again and again, as its various commercial residents (a laundry, prior to the steelworks) had expanded. A warehouse-sized workshop had been built to the rear and two neighbouring gardens sequestered for yet more extensions, creating a great L-shaped sprawl.

"It was daunting when we first saw the buildings still full of the steel fabricator's stuff, yet as soon as it was stripped back it felt enormous and the possibilities were all there," Tuckey says. "Something about that main shell felt very precious, and the new really grew out of the old."

Having decided to preserve the main warehouse as a centre point for the house, Tuckey set about configuring the living space. A mezzanine was created at one end of the warehouse, with the sitting room below and a guest bedroom and study above, with space left to one side for the high, sculpted chimney buttress and skylight. The smaller sheds at the back of the site were removed to make way for the garden and the new-build element - a two-storey structure clad in larch plywood with master bedroom above and the girls' bedroom below. It is connected to the rest of the house by a slim corridor, with glass walls that open to the garden.

"In the spring and summer the girls start their day by opening up their door to the courtyard. The first thing we hear is the sound of them playing in the garden."

With double-height ceilings, raw brick walls and long skylights, the family's hangar-sized kitchen is the hub of the house. In summer, the glass doors are opened out and the family eats in the quiet of the garden. Tuckey has defied convention with a few innovations in his home. He has placed a tap near the dinner table, which saves having to get up for a glass of water and also feeds a small channel in the concrete floor that flows into the garden.

The bathroom, an open-plan wet room which is under the stairs in the new bedroom block, has a deep tiled tub that is fed by three copper pipes, one cold, two hot, and there's no electric light. In their old house, in Harlesden, the transformer in the bathroom kept cutting out, so they bathed only by candlelight. Anxious to preserve the ritual, they consciously left out the electrics. "At the weekends, we are in that bathroom for two hours every evening," says Tuckey. "It's really used as we imagined it would be - for chatting and reading, as well as washing, and with the children making runways out of night lights on the floor."

The rugged simplicity continues with underheated concrete floors in the main space, exposed copper pipes and taps, enamelled sinks and worktops, and the plain brickwork.

"Being a designer, there was a sense in which I didn't want it to appear completely finished," says Tuckey. "With most projects, you hand the house over to a client and never see it again, but this is something we're living in and that we wanted to be more organic - more of a framework in which to live our lives. Also, over-designed elements such as beautiful taps or light switches are often installed as apologies for a badly designed space, and it was partly a reaction against that. This place is about using simple materials in a way that's unusual and innovative. It was probably also determined by cost, but I wouldn't have it any other way."